Smartphone-based alarm clocks have become increasingly sophisticated and featured-packed, and more and more people are ditching their old-school alarms for alarms of the app variety. Here are five of the most popular mobile alarm apps.

Earlier this week we asked you to share your favorite mobile alarm apps, and now we're back to highlight the five most popular apps, including the features that make them favorites. (Note: Many of you just stick with your mobile OS default; that's fine, but for the purpose of this post, we're featuring alternatives.)

Sleep Cycle is a popular iOS alarm clock that turns your iPhone or iPod touch into a motion-sensitive alarm clock. Instead of merely keeping track of what time it is and when you want to wake up, Sleep Cycle uses the accelerometer in the device to measure when you're moving in your sleep. It uses this record of tossing, turning, and adjusting yourself in your sleep to track when you are in deep sleep and when you are in lighter sleep, ready to be woken up. If you need to be up at 7:00AM, for example, and Sleep Cycle detects you are stirring and ready to be woken at 6:32, it will gently wake you up instead of letting you slide back into deeper sleep and jarring you awake at 7:00. [iTunes App Store]

Gentle Alarm is a veritable Swiss Army knife of alarm clock functionality. You can set multiple alarms and customize alarm type, length, and modulation. Gentle Alarm supports profiles so you can quickly switch between using the alarms for your nightly sleep as well as power naps and other timer functions. Gentle Alarm includes a sleep cycle monitor that uses pre-alarms to wake you when you are most likely to be in light sleep and will wake up refreshed. If you're prone to hitting the snooze button, Gentle Alarm's optional lock system forces you to repeat a complex unlock pattern—similar to the Android lock screen—to make sure you wake up. The free trial includes all the functionality of the pay version, except the alarms are disabled on Wednesdays. [AppBrain]

Alarm Clock Plus is an Android alarm app that includes an enormous number of customizable features. You can create alarm playlists to wake up to music, select ringtones from your phone as alarms, set the number of snoozes (if any) and even configure the phone to quiz you with math problems to disable the alarm. The default "dock" screen displays the weather as well as quick access to photo slide shows and your music player. You can even configure Alarm Clock Plus to launch applications based on system alarms—so you could launch your news reader, email, or other application right after your alarm went off. [AppBrain]

G-Alarm is a serious replacement for the lack-luster default alarm in Windows Mobile. It supports multiple alarms, wake-up playlists, a skinnable interface, alarm export for easy backup, scheduled application launching, and alarm-based puzzles like solving math problems and/or navigating a ball through a randomly generated maze. G-Alarm also takes advantage of the sensors in the phone, you can shake or flip over your phone to snooze an alarm or shut it off completely. G-Alarm has a 10-day trial period.

While motion sensors, music playlists, and math-based snooze buttons are pretty neat, some people just want an alarm app that's an improved version of the default without all the wild features. Alarm Klock is similar to the default Android alarm app but enhanced with features like per-alarm settings, MP3 alarms instead of just phone ringtones, variable snooze, and alarm volume adjustment independent of the phone ringers. [AppBrain]

Now that you've seen the most popular mobile alarm apps, it's time to cast a vote for your favorite: